A generic type of apparatus for manufacturing die-castings is disclosed in German patent DE 30 02 886 C2. In this apparatus, as in other prior art diecasting machines equipped with evacuation means for evacuating the casting molds, filling the mold with molten metal for the last time takes place within a few milliseconds and simultaneously with the evacuation of said mold. The aim here is to obtain a vacuum as high as possible in the mold cavity of the diecasting mold so as to ensure that the finished die-casting is of maximum quality.
European patent no. 0 600 324 A1 describes a method for generating a vacuum in a vacuum diecasting machine in which the vacuum to be generated in the diecasting mold may be controlled during the actual casting process. The march of the pressure of the vacuum generated is controlled via a vacuum valve such that the pressure in the mold cavity, in the casting chamber and in the suction tube is controlled according to a certain variable function per unit of time. The negative pressure is detected via a vacuum measuring probe which measures the pressure in a vacuum connection line.
A pressure diecasting method, however, also requires the use of separating agents and lubricants. The primary task of such additives is to provide a separating layer between the molten metal and the contours of the casting mold, thus preventing the metal from adhering to the casting mold. This happens especially in the case of aluminum diecasting due to the high affinity of the aluminum for the iron of the casting mold. Conventionally, water-mixable separating agents are used for generating said separating layer. These separating agents additionally have a cooling or tempering effect on the diecasting mold.
However, a disadvantage inherent to these prior art methods or apparatuses is that, once the die-cast part has been removed from the mold, the separating agent(s) will have to be deposited anew and that, when the diecasting mold is blown dry, some residual moisture will remain in the mold cavity. While it is possible to suck off a certain percentage of this residual moisture, together with other gases generated during casting, from the mold cavity in the evacuation step, some residual moisture will always remain in the diecasting mold. In a subsequent casting step, however, such residual moisture in the diecasting mold will react adversely with the molten metal, thereby again generating gases. The formation of gases in turn will result in the finished die-casting to be porous or in blowholes or bubbles to be present therein. This will considerably diminish the quality of the finished diecasting.